From a Location Service to a Multicast Service for Wireless Mobile Adhoc Networks

In this paper we propose a novel approach for multicasting in Mobile Ad-hoc Networks (MANETs). Since no fixed infrastructure of servers is assumed in MANETs, efficient location management schemes are necessary in order to store and provide information about various services offered throughout the network. MDLM is the first multicast algorithm relying on a location management service. We thus avoid fragile data structures such as trees or DAGs to manage multicast groups, without reverting to more reliable, yet overhead-prone mesh-based algorithms

Position-Based Multicast for Mobile Ad-hoc Networks

In general, routing protocols for mobile ad-hoc networks (MANETs) can be classified into topology-based protocols and position-based protocols. While for unicast routing many proposals for both classes exist, the existing approaches to multicast routing basically implement topology-based algorithms and only a few of them make use of the geographic positions of the network nodes. These have in common that the sending node has to precalculate the multicast tree over which the packets are distributed and store it in each packet header. This involves two main issues: (a) These approaches are not very flexible with regard to topological changes which abandons the advantages that position-based routing has against topology-based routing, and (b) they do not scale with the number of receivers, since every one of them has to be named in the packet header. This thesis solves these issues and further advances position-based multicast routing. Position-Based Multicast (PBM) enhances the flexibility of position-based multicast routing by following the forwarding principle of position-based unicast routing. It transfers the choice of the next hops in the tree from the sender to the forwarding nodes. Based on the positions of their neighboring nodes, these are able to determine the most suitable next hop(s) at the moment when the packet is being forwarded. The scalability with respect to the number of receiving nodes in a group is solved by Scalable Position-Based Multicast (SPBM). It includes a membership management fulfilling different tasks at once. First, it administers group memberships in order to provide multicast sources with information on whether nodes are subscribed to a specific group. Second, it implements a location service providing the multicast sources with the positions of the subscribed receiver nodes. And third, it geographically aggregates membership data in order to achieve the desired scalability. The group management features two modes of operation: The proactive variant produces a bounded overhead scaling well with the size of the network. The reactive alternative, in contrast, reaches low worst-case join delays but does not limit the overhead. Contention-Based Multicast Forwarding (CBMF) addresses the problems that appear in highly mobile networks induced by outdated position information. Instead of basing forwarding decisions on a perception that may no longer be up to date, the packets are addressed only to the final destination; no explicit next hops are specified. The receiving nodes, which are candidate next hops, then decide by means of contention which of them are the most suitable next hop(s) for a packet. Not only is the decision made based on the most currently available data, but this procedure also saves the regular sending of beacon messages, thus reducing the overhead. The lack of multicast congestion control is another unsolved problem obstructing high-bandwidth data transmission. Sending out more and more packets to a multicast group lets the performance decrease. Backpressure Multicast Congestion Control (BMCC) takes care that the network does not need to handle more packets than it is able to. It achieves this by limiting the packet queues on the intermediate hops. A forwarder may not forward the next packet of a stream before it has noticed---by overhearing the transmission of the next hop---that the previous packet has succeeded. If there is congestion in an area, backpressure is implicitly built up towards the source, which then stops sending out packets until the congestion is released. BMCC takes care that every receiving node will receive packets at the same rate. An alternative mode of operation, BMCC with Backpressure Pruning (BMCC-BP) allows the cutting of congested branches for single packets, permitting a higher rate for uncongested receivers. Besides presenting protocols for multicast communication in MANETs, this thesis also describes implementations of two of the above-mentioned protocols. The first one is an implementation of SPBM for the Linux kernel that allows IP applications to send data via UDP to a group of receivers in an ad-hoc network. The implementation resides between the MAC layer and the network/IP layer of the network stack. It is compatible with unmodified standard kernels of versions 2.4 and 2.6, and may be compiled for x86 or ARM processor architectures. The second implementation is an implementation of CBMF for the ScatterWeb MSB430 sensor nodes. Due to their low-level programmability they allow an integration of the routing protocol with the medium access control. The absence of periodic beacon messages makes the protocol especially suitable for energy-constrained sensor networks. Furthermore, other constraints like limited memory and computational power demand special consideration as well